I should really listen to my own advice more...

[djnotts]

"It's a got a lot more to do with design, execution and circumstance than material."

+1.

[Keezx]

Poor construction of that frame....
I guess the designer/builder of that frame never saw this animation, it shows that the lower gussset is completely unnecessary:

[De Sisti]

I've lost count of the amount of times I've advised people not to ignore creaks and clicks and to attend to them quickly in case you either make a small problem into a big one over time, or in case it's hiding something more catastrophic in the making.

So what have I been doing for the last 2-3 weeks? Yup, that's right, stubbornly ignoring the ever increasing volume of the clicking and creaking coming from my commuter.

Well it got a bit louder again this morning, and was happening while seated as well as standing and then I got a little bit of shimmy going down one of the hills on the way to work, alarm bells started ringing in my head so I stopped to check it over and discovered the crack that has now propagated about 1/3rd of the way around the downtube

Suffice it to say the rest of the trip was taken at a sedate pace and I'll be paying more attention to my own advice in future. Another commuter bites the dust

I had a similar encounter about five years ago on one of my short hilly rides. I assumed it was the bottom bracket and had decided
to attend to it when I retturned home. When I put the bike on the maintenance stand to attend to it I noticed an almighty crack
around the bottom of the down tube/seat tube.

[amediasatex]

I guess the designer/builder of that frame never saw this animation, it shows that the lower gussset is completely unnecessary:

Whether or not the original design is flawed* I think you're being overly simplistic there and assuming you can port one FEA/set of calcs from one design to another when you can't.

That animation shows where the stress locations are on that frame, under that loading scenario (which are not quantified) but that frame has substantial differences in build, let alone possible differences in material and individual tube spec that are not evident without further information. Note the front end in that animation is built very differently and clearly not built from small diameter steel.

If you build up or beef up one area you'll move stresses elsewhere, or at least mean the relative 'peaks' are seen elsewhere. ie: massively beef up the front end and the peaks will now seem to be elsewhere, BB for example, even if the value you're observing isn't much different to what it would have been with the original front end, ie: you've designed and mitigated the stresses at the front end, so if you just looked at that animation in isolation you might assume the front end/head tube junction of a bike is not massively stressed, but the reality is that it is (or at least can be under some load sceanrios), but that frame has already been built to reduce them. Likewise this frame that failed is an MTB frame and intended to be used offroad with suspension forks, very different kettle of fish to a road racing frame.

* This frame broke due to a dodgy weld, possibly exacerbated due to the gusset design but that's still conjecture and opinion form us, as we don't have access to any of the original calcs or FEA. Although the design may be improvable it doesn't mean it was necessarily poor. There are many other examples of this frame out in the wild getting far harder use than I have given this one that have not yet failed, of course they may do at some point but clearly the frame design is not unfit for purpose and it would have passed CEN tests etc.

[Keezx]

So you don't think gussets thicker than frame tubes are a stupid idea?
So buy another similar frame ....

[amediasatex]

So you don't think gussets thicker than frame tubes are a stupid idea?
So buy another similar frame ....

That is not what I said at all. Please don't attempt to put words in my mouth in order to start an argument, the tone of your post is both adversarial and condescending and I have no idea why...

FWIW, It's also not a question you asked, you said :

I guess the designer/builder of that frame never saw this animation, it shows that the lower gussset is completely unnecessary:

And as above, I think that's an overly simplistic view as the animation doesn't tell you much about frames or gussets 'in general', nor much at all about the specific frame that has failed, all it does is demonstrate the stresses on that frame design, under that loading scenario.

A single instance of a failure, analysed in retrospect, remotely via photos is an interesting thing to discuss for sure, but cannot be reliably extrapolated out to suggest that all frames of the same design are likely to suffer the same failure, and indeed anecdotally it appears there is evidence to the contrary. I think it's also unfair to comment on the skills of the designer (who I have no personal relationship with BTW, so no reason to defend) when none of us are in possession of the full facts, let alone full specs of the tubing or any calculations, testing or FEA analysis done on the frame design before general sale to the public.

I personally know at least 3 people with the same frame, 2 of whom have owned theirs longer than me. It's also a production model of which many units were sold, they don't have a documented history of multiple failures (yet) so for the moment I'm filing this under 'dodgy weld exacerbated by sub-optimal gusset', but I'm not extrapolating out to 'dodgy design, avoid' as that seems both overly alarmist and premature.

[fastpedaller]

It looks to me as if the gusset is much longer than others (ooer)
If the tubing is butted, could some of the weld be at a thinner part of the tube (rather than the thicker end part)?
I've been puzzled in the past by 'super long' lugs on brazed frames, which (it would appear) may cause heating of a thin section of tube which is probably best to avoid?

[amediasatex]

If the tubing is butted, could some of the weld be at a thinner part of the tube

It's entirely possible but none of us have the tubeset or design specs to confirm...having said that it would be unusual for a manufacturer to make such a rookie error as running a gusset past the end of the butting.

[amediasatex]

Happy ending! Frame was collected by courier yesterday (at retailers cost) and retailer has refunded me my original payment as no suitable alternative replacement was available.

That's pretty good service in my book, failures happen, hopefully rarely but how retailers deal with warranty cases can really make or break the experience.

[mig]

Happy ending! Frame was collected by courier yesterday (at retailers cost) and retailer has refunded me my original payment as no suitable alternative replacement was available.

That's pretty good service in my book, failures happen, hopefully rarely but how retailers deal with warranty cases can really make or break the experience.

good stuff.

buying a replacement then?

[amediasatex]

Not for the moment, I'm fortunate enough to have (too) many bikes so using my tourer to commute and have another (same frame as the tourer) spare in the loft that I'm going to start acquiring bits for and will build that up in time with a slightly more 'utility bike' approach.

Some bits from the broken bike will fit but wheels are different size so will need re-rimming at least...

Although I might use this as an excuse to start saving for that long-nose cargo bike I've been threatening to buy for a while